1. Field of the Invention
The present invention relates to a remote control for a locking device, especially in a motor vehicle, including a control or operating unit for the transmitting of key words to the evaluating circuit of a reading unit fora comparison with key words which are stored therein.
2. Discussion of the Prior Art
A remote control unit or arrangement of that kind is already known from the disclosure of European Laid-Open Patent Appln. No. 0 153 498 in the form of a contactless remote actuating system for door locking assemblies; and especially for the central locking arrangement employed in a motor vehicle. Upon actuation of the control or operating unit, there is emitted electromagnetic radiation, wherein this radiation is assumed by the receiver of a reading unit which is installed in the motor vehicle, in order to compare the received and demodulated key word with a stored password key word. A pulse position-modulation is employed for the transmission of the key word.
With regard to infra-red remote control or operating units which are currently available on the market for the actuation of the central locking arrangement of a motor vehicle, it is known to store different key words in the same sequence at both the transmitting end as well as at the receiving end, and to switch forward within the control unit by one memory address to the subsequently following key word after each manual actuation of the control unit. The foregoing procedure is intended to prevent an unauthorized person from gaining access to the key word which is actually being used for the opening of the vehicle, in order to be able on his part to open the vehicle through a reproduction of that key word. This is because the successive key word now differs from the previous key word, and an outsider cannot ascertain when the key word which was randomly accessed in an unauthorized manner will again be available in its series. The forward shifting of the key word within the memory of the vehicle takes place each time whenever a correct key word has been received and has led to an enable or release signal for the switching over in the condition of the locking device. However, because it is quite possible that the user of the control or operating unit actuates the switch and thereby initiates the forward switching of key word at the transmitting end, whereas, on the other hand, inexpedient transmitting conditions do not lead to a verification of this key word in the reading unit, a group of successively following key words will always be compared at the receiving end with the current or actually received key word with regard to correlation contained therein, and thereafter the address access is set, as necessary, at the receiving end to the key word which is actually applicable.